feat(map): self-hosted PMTiles map tiles, remove alert toast spam

- Replace OpenStreetMap CDN with self-hosted Protomaps PMTiles
  (Wisconsin + Florida regional extracts, served from nginx)
- Add protomaps-leaflet for vector tile rendering in dark theme
- Update CSP to remove openstreetmap.org, add blob: for vector workers
- Add nginx location block for /tiles/ with byte range support
- Mount tiles directory as volume (not baked into image)
- Remove alert_fired/alert_resolved toast notifications that spammed
  "undefined" at fleet scale — dashboard still updates via query invalidation
- Add *.pmtiles to .gitignore (large binaries)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/package.json

@@ -50,6 +50,7 @@
     "framer-motion": "^12.34.3",
     "leaflet": "^1.9.4",
     "lucide-react": "^0.575.0",
+    "protomaps-leaflet": "^5.1.0",
     "react": "^19.2.0",
     "react-dom": "^19.2.0",
     "react-leaflet": "^5.0.0",